1. Field of the Invention
The present invention relates to piconet wireless networks. More particularly, it relates to baseband clock generation for BLUETOOTH™ radio frequency (RF) integrated circuits.
2. Background of Related Art
Piconets, or small wireless networks, are being formed by more and more devices in many homes and offices. In particular, a popular piconet standard is commonly referred to as a BLUETOOTH piconet. Piconet technology in general, and BLUETOOTH technology in particular, provides peer-to-peer communications over short distances.
The wireless frequency of piconets may be 2.4 GHz as per BLUETOOTH standards, and/or typically have a 20 to 100 foot range. The piconet RF transmitter may operate in common frequencies which do not necessarily require a license from the regulating government authorities, e.g., the Federal Communications Commission (FCC) in the United States. Alternatively, the wireless communication can be accomplished with infrared (IR) transmitters and receivers, but this is less preferable because of the directional and visual problems often associated with IR systems.
A plurality of piconet networks may be interconnected through a scatternet connection, in accordance with BLUETOOTH protocols. BLUETOOTH network technology may be utilized to implement a wireless piconet network connection (including scatternet). The BLUETOOTH standard for wireless piconet networks is well known, and is available from many sources, e.g., from the web site www.bluetooth.com.
According to the BLUETOOTH specification, BLUETOOTH systems typically operate in a range of 2400 to 2483.5 MHz, with multiple RF channels. For instance, in the US, 79 RF channels are defined as f=2402+k MHz, k=0, . . . , 78. This corresponds to 1 MHz channel spacing, with a lower guard band (e.g., 2 MHz) and an upper guard band (e.g., 3.5 MHz).
To receive a radio frequency (RF) signal from another piconet device, the receiving device must lock onto the transmitted frequency. All receiving devices have a local clock on which a baseband receive clock signal in an RF section is based.
Currently, there are two RF interface standards for the RF section of BLUETOOTH devices: Blue-Q from QUALCOMM INC. and Blue-RF from the Bluetooth RF Committee. Blue-Q uses a 12 MHz clock for baseband and oversampling clock signals. Blue-RF, the other current BLUETOOTH RF standard, uses a 13 MHz clock for baseband and oversampling clock signals. BLUETOOTH RF integrated circuits are designed based either on a 12 MHz clock signal (Blue-Q), or on a 13 MHz clock signal (Blue-RF).
It is important to note that in the real world, clock signals jitter and vary somewhat within desired tolerable limits. Other than the frequency requirements, the BLUETOOTH standard specifies that the clock jitter (rms value) should not exceed 2 nS and the settling time should be within 250 uS. A significant source of clock variation is the variance between external crystal oscillators installed in any particular BLUETOOTH device. Temperature also causes variations in clock signals.
To meet these very tight limits, a system designer must optimize receive circuits based on the particular clock speed for which the system is designed (e.g., 12 MHz or 13 MHz). Thus, to support devices in both standards, an integrated circuit manufacturer must design and offer two distinct BLUETOOTH RF integrated circuits: one based on a 12 MHz clock, and another based on a 13 MHz clock.
There is a need for a simplified approach to support RF portions of piconet devices in general, and BLUETOOTH devices in particular.